Step No. 2
This step is for drums which tension the head via a balanced mechanism. Observing the MSR, decide the lowest pitch and the highest pitch at which you want the instrument to sound. The lowest note chosen can also affect the available highest note on the drum and the efficiency of the balanced action mechanism so please check the manual which came with your timpani for the suggested range for each drum. Sometimes it is beneficial to set the highest notes you will need on the drum and let the low notes fall where they may. Some American models of timpani featuring the balanced action mechanism tend to have less range than some later European models which advertise an octave range. The overall range may be affected by the type of heads you are using. Some manufacturers heads purportedly have a narrower range than other manufacturers which may limit the range of the timpani suggested by the manufacturer. Please check the manual for any head specifications.
Sample MSR pitches for various timpani are:
32″ drum – D, 29″ drum – F, 26″ drum-B-flat, 23″ drum-D
Other Manufacturers Recommend 
The size of the drum is generally determined by the diameter of the bowl, not by the diameter of the head or the counterhoop. To determine the size of the bowl, measure the lip of the bowl (the bearing edge) at opposing tension lug points.
The size of the head is determined by the counterhoop. Some timpani manufacturers use non-standard counterhoop sizes. Be sure to consult the owner’s manual for the correct size of heads needed for your instruments before ordering replacement heads.